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      Intranasal Insulin to Improve Memory Function in Humans

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          Background: Compelling evidence indicates that central nervous insulin enhances learning and memory and in particular benefits hippocampus-dependent (i.e., declarative) memory. Intranasal administration of insulin provides an effective way of delivering the compound to the central nervous system, bypassing the blood-brain barrier and avoiding systemic side effects. Methods: Here we review a series of recent studies on the effects of intranasally administered insulin on memory functions in humans. In accordance with the beneficial effects of intravenously administered insulin on hippocampus-dependent declarative memory observed in hyperinsulinemic-euglycemic clamp studies, intranasal insulin administration similarly improves this type of memory, but in the absence of adverse peripheral side effects. Result and Conclusion: Considering that cerebrospinal fluid insulin levels are reduced in patients suffering from Alzheimer’s disease, these results may be of considerable relevance for future clinical applications of insulin in the treatment of memory disorders.

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          Most cited references 40

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          Hippocampus: cognitive processes and neural representations that underlie declarative memory.

          The hippocampus serves a critical role in declarative memory--our capacity to recall everyday facts and events. Recent studies using functional brain imaging in humans and neuropsychological analyses of humans and animals with hippocampal damage have revealed some of the elemental cognitive processes mediated by the hippocampus. In addition, recent characterizations of neuronal firing patterns in behaving animals and humans have suggested how neural representations in the hippocampus underlie those elemental cognitive processes in the service of declarative memory.
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            Obesity in middle age and future risk of dementia: a 27 year longitudinal population based study.

            To evaluate any association between obesity in middle age, measured by body mass index and skinfold thickness, and risk of dementia later in life. Analysis of prospective data from a multiethnic population based cohort. Kaiser Permanente Northern California Medical Group, a healthcare delivery organisation. 10,276 men and women who underwent detailed health evaluations from 1964 to 1973 when they were aged 40-45 and who were still members of the health plan in 1994. Diagnosis of dementia from January 1994 to April 2003. Time to diagnosis was analysed with Cox proportional hazard models adjusted for age, sex, race, education, smoking, alcohol use, marital status, diabetes, hypertension, hyperlipidaemia, stroke, and ischaemic heart disease. Dementia was diagnosed in 713 (6.9%) participants. Obese people (body mass index > or = 30) had a 74% increased risk of dementia (hazard ratio 1.74, 95% confidence interval 1.34 to 2.26), while overweight people (body mass index 25.0-29.9) had a 35% greater risk of dementia (1.35, 1.14 to 1.60) compared with those of normal weight (body mass index 18.6-24.9). Compared with those in the lowest fifth, men and women in the highest fifth of the distribution of subscapular or tricep skinfold thickness had a 72% and 59% greater risk of dementia, respectively (1.72, 1.36 to 2.18, and 1.59, 1.24 to 2.04). Obesity in middle age increases the risk of future dementia independently of comorbid conditions.
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              Delivery of insulin-like growth factor-I to the rat brain and spinal cord along olfactory and trigeminal pathways following intranasal administration.

              We investigated the CNS delivery of insulin-like growth factor-I (IGF-I), a 7.65 kDa protein neurotrophic factor, following intranasal administration and the possible pathways and mechanisms underlying transport from the nasal passages to the CNS. Anesthetized adult male Sprague-Dawley rats were given [125I]-IGF-I intranasally or intravenously and then killed by perfusion-fixation within 30 min. Other animals were killed following cisternal puncture and withdrawal of cerebrospinal fluid (CSF) or intranasal administration of unlabeled IGF-I or vehicle. Both gamma counting of microdissected tissue and high resolution phosphor imaging of tissue sections showed that the tissue concentrations and distribution following intranasal administration were consistent with two routes of rapid entry into the CNS: one associated with the peripheral olfactory system connecting the nasal passages with the olfactory bulbs and rostral brain regions (e.g. anterior olfactory nucleus and frontal cortex) and the other associated with the peripheral trigeminal system connecting the nasal passages with brainstem and spinal cord regions. Intranasal administration of [125I]-IGF-I also targeted the deep cervical lymph nodes, consistent with their possible role in lymphatic drainage of both the nasal passages and the CNS. Cisternal CSF did not contain [125I]-IGF-I following intranasal administration. Intravenous [125I]-IGF-I resulted in blood and peripheral tissue exposure similar to that seen following intranasal administration but CNS concentrations were significantly lower. Finally, delivery of IGF-I into the CNS activated IGF-I signaling pathways, confirming some portion of the IGF-I that reached CNS target sites was functionally intact. The results suggest intranasally delivered IGF-I can bypass the blood-brain barrier via olfactory- and trigeminal-associated extracellular pathways to rapidly elicit biological effects at multiple sites within the brain and spinal cord.

                Author and article information

                S. Karger AG
                September 2007
                20 July 2007
                : 86
                : 2
                : 136-142
                aDepartment of Neuroendocrinology and bInternal Medicine I, University of Lübeck, Lübeck, Germany; cInterdisciplinary Obesity Center East Switzerland, Kantonsspital St. Gallen, St. Gallen, Switzerland
                106378 Neuroendocrinology 2007;86:136–142
                © 2007 S. Karger AG, Basel

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                Page count
                Figures: 3, Tables: 1, References: 53, Pages: 7


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